1. Field of the Invention:
This invention relates generally to surgical apparatus for use in the conduct of transluminal angioplasty or transluminal angiography procedures, and more particularly to the design of a blood pressure monitoring catheter especially designed for use in a Monorail.TM. type catheter system.
2. Discussion of the Prior Art:
In diagnosing and treating coronary artery disease, a technique called transluminal angiography may first be used to assess the extent and nature of the buildup of stenotic lesions within the vascular system. One important parameter useful in such assessment is the pressure gradient across a lesion. When the gradient is low, it is known that the lesion may not be seriously occluding the blood vessel. Where, however, the pressure gradient is high, it is known that the occlusion is significant and a candidate for immediate treatment.
One method of treatment of stenotic lesions in the vascular system is the use of so-called transluminal balloon angioplasty. In carrying out this procedure, an elongated, flexible, plastic catheter having an inflatable expander member proximate its distal tip is introduced at an appropriate site in the vascular system, usually in the femoral artery, and routed through the system to the site of the lesion to be treated. Once the uninflated expander is positioned across the lesion to be treated, an appropriate fluid is introduced into the proximal end of the catheter and it flows to inflate the balloon and compress the stenotic lesion against the walls of the blood vessel.
Two types of catheter systems are recognized in the art. The first is referred to as an over-the-wire catheter in which the catheter has a lumen extending its entire length from its distal end to its proximal end. Following the insertion of a guide catheter through the vascular system such that its distal end is located near the site to be treated, a guidewire is routed through the guide catheter and by manipulating the proximal end of the guidewire, an attempt is made to cause its distal end to cross the stenotic lesion to be treated. Following that, a balloon angioplasty catheter is fitted over the guidewire by having the guidewire pass through the lumen which runs the length of the catheter. These over-the-wire catheters have proven somewhat difficult to work with, especially when it comes to the need to exchange one working catheter for another. Moreover, because the guidewire is totally contained within the entire length of the working catheter, a relatively high frictional resistance tends to be present when advancing or retracting the working catheter relative to the guidewire. In fact, because of this frictional drag, it has happened that during an exchange maneuver, the guidewire is actually dislodged from its site across the stenotic lesion, thus requiring the surgeon to again go through a repositioning procedure.
To obviate certain of the problems associated with the over-the-wire catheter system, a subsidiary of applicant's assignee has developed a Monorail.TM. catheter system. Here, rather than running a guidewire completely along the interior lumen of the working catheter, a relatively short tubular segment is provided near the distal end of the working catheter for receiving the guidewire. Thus, rather than being totally enclosed with the wall of the working catheter over its entire length, in the Monorail.TM. catheter system, only a very short length of tubing surrounds the guidewire near the distal end of the working catheter. The guidewire then extends parallel to and along side the outer diameter of the working catheter as the two extend in the proximal direction through the guiding catheter. Details of the Monorail.TM. catheter construction are set out in the Bonzel U.S. Pat. No. 4,762,129, and those desiring further information relative to the overall features and advantages of Monorail.TM. catheters are referred to that patent.
The present invention is directed to a blood pressure monitoring catheter especially designed for use in a Monorail.TM. catheter system for assessing the pressure gradient across a stenotic lesion. The blood pressure monitoring catheter of the present invention thus comprises an elongated, flexible, plastic, bi-lumen, extruded, tubular member having a guidewire port extending through the wall thereof to intersect with one of the two lumens, the port being a relatively short distance proximal of the distal end of the tubular member. A plug is inserted into this one lumen at a point proximal of the guidewire port. The other lumen of the bi-lumen catheter runs the entire length of the tubular member from its distal end to its proximal end. The proximal end is fitted with a molded plastic hub to facilitate the attachment of the catheter to the auxiliary equipment used to measure, monitor and record blood pressure readings.
In use, once a guidewire has been positioned across the stenotic lesion and it is desired to take a blood pressure measurement, the proximal end of the guidewire may be fitted into the distal end of the first lumen and fed through it until the guidewire exits the guidewire port. Holding on to the proximal end of the guidewire, the physician may push the blood pressure monitoring catheter through the guide catheter and, in doing so, the blood pressure monitoring catheter will ride along the guidewire until its distal end is on one side or the other of the stenotic lesion. The proximal end of the blood pressure monitoring catheter is then connected to the blood pressure measuring equipment and a first reading taken. The blood pressure monitoring catheter is then repositioned on the opposite side of the stenotic lesion and a second reading is taken. Having the two readings, the gradient across the stenotic lesion is determined.
Alternatively, the catheter may include two blood pressure measuring lumens, one exiting the distal end of the catheter and the other ending proximally a predetermined distance from the distal end and with a port extending through the wall of the catheter in fluid communication with the shorter lumen. Readings can be simultaneously taken through both lumens without moving the catheter.